The aim of this study is to investigate the effectiveness of Conners Rating Scale in assessing attention deficit hyperactivity disorder (ADHD) in primary school bos in different demographic areas of Tehran city. The study consisted of an experimental group (n=36) comprising of subjects satisfying DSM-III-R criteria for ADHA. These subjects were drawn from different psychiatric clinics. The normal control group (n=36) was matched on the relevant control variables with the experimental group. Results indicate that the Conners Rating Scale is a valid measure for discriminating ADHD from normals.